Break-off drillpoint screw

ABSTRACT

A fastener, method of fastening, a fastener and drive tool system, and a drive tool for driving a fastener in which the fastener has a leading portion or drill tip portion which is frangible and detachable from the threaded portion. The fastener includes a shank having a head formed at one end, the leading portion or drill tip at an opposite end thereof, and the threaded portion positioned intermediate the head and drill portion. A weakened or frangible portion is provided on the shank between the drill tip and the threaded portion for dividing the fastener into the threaded portion which is retained in engagement with the workpieces and the drill tip which is detached from the fastener. The method includes driving the fastener into a workpiece and detaching or fracturing the drill tip from the threaded portion generally at a predetermined location. The detachment or frangible portion is formed to facilitate fracture at a predetermined area along the shank either manually or automatically as a function of the structure of the fastener and/or the fastener driving process. The present invention also includes the tool included in the fastener system which is used to drive the fastener into a workpiece. The tool includes an interference block having a surface which promotes fracture and detachment of the drill from the threaded portion when the drill portion abuts and is deflected by the surface.

BACKGROUND

The present invention relates to self-drilling fasteners having a drillportion which is detachable or frangible from a threaded portion, amethod of fastening using a self-drilling fastener of the presentinvention, and a drive tool for use with a self-drilling fastener of thepresent invention.

Numerous fasteners are available which provide self-drilling features.In many applications, self-drilling fasteners, such as drill screws, areadvantageous as the holes and threads are drilled and formed by thefastener in a single driving application. Self-drilling fastenerseliminate the additional assembly steps of drilling and tapping holesbefore driving of the fastener. As such, self-drilling fasteners may behighly advantageous by reducing preparation and assembly time, cost andeffort.

Self-drilling fasteners are designed with a shank having a head formedat one end, a drill-tip portion at the end opposite the head, and athreaded portion intermediate the drill portion and head. The drill-tipportion is provided with a chisel point and cutting edge which drillinto the workpiece material forming a hole for engagement by thethreaded portion. The drill portion is sized and dimensioned to providea hole having a predetermined diameter which provide positive engagementof the thread portion, for cold forming or swaging internal threadsthereon.

While self-drilling fasteners of the type briefly described hereinabovehave provided many advantages, use of such fasteners in some situationsmay not provide desirable finished results. For example, in applicationswhere the thickness dimension of the workpiece is less than the totallength of the shank of the fastener, the drill-point may protrude fromthe workpiece. This may be undesirable as it may result in a pointextending from a surface or may merely appear to be unfinished orotherwise aesthetically undesirable. Additionally, the drill-point isnot required in the workpiece since often it does not include threadsand therefore does not provide substantial mechanical advantage or anyclamping function in joining the workpieces, as compared to the threadedportion.

OBJECTS AND SUMMARY

A general object satisfied by the invention is to provide a fastenerwhich includes a drill portion or drillpoint which is detachable fromthe shank of the fastener.

Another object satisfied by the invention may be to provide a method offastening in which a fastener is driven into a workpiece and thedrilling portion is detached from the threaded portion at some pointeither during or after the fastener is driven into the workpiece.

Briefly, and in accordance with the foregoing, the present inventionenvisions a fastener, method of fastening, a fastener and drive toolsystem, and a drive tool for driving a fastener in which the fastenerhas a leading portion or drill tip portion which is frangible anddetachable from the threaded portion. The fastener includes a shankhaving a head formed at one end, the leading portion or drill tip at anopposite end thereof, and the threaded portion positioned intermediatethe head and drill portion. A weakened or frangible portion is providedon the shank between the drill tip and the threaded portion for dividingthe fastener into the threaded portion which is retained in engagementwith the workpieces and the drill tip which is detached from thefastener. The method includes driving the fastener into a workpiece anddetaching or fracturing the drill tip from the threaded portiongenerally at a predetermined location. The detachment or frangibleportion is formed to facilitate fracture at a predetermined area alongthe shank either manually or automatically as a function of thestructure of the fastener and/or the fastener driving process. Thepresent invention also includes the tool included in the fastener systemwhich is used to drive the fastener into a workpiece. The tool includesan interference block having a surface which promotes fracture anddetachment of the drill from the threaded portion when the drill portionabuts and is deflected by the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The organization and manner of the structure and function of theinvention, together with further objects and advantages thereof, may beunderstood by reference to the following description taken in connectionwith the accompanying drawings, wherein like reference numerals identifylike elements, and in which:

FIG. 1 is an enlarged, partial fragmentary, cross-sectional, sideelevational view of a fastener of the present invention positioned forinsertion into a joint formed by two workpieces;

FIG. 2 is an enlarged, partial fragmentary, cross-sectional, sideelevational view of the fastener inserted into but not fully driven intoand seated in the workpieces;

FIG. 3 is an enlarged, partial fragmentary, cross-sectional, sideelevational view in which the fastener is completely driven into andseated in the workpieces and a leading portion of the fastener has beenfractured and detached from a portion which is retained in theworkpieces;

FIG. 4 is a partial fragmentary, cross-sectional, side elevational viewof a fastener of the present invention employed in a use to attach amolding strip to a body portion having two flanges forming anoverlapping joint;

FIG. 5 is a partial fragmentary, cross-sectional, side elevational viewof the workpiece as shown in FIG. 4 further including a tool andinterference assembly which facilitates driving of the fastener into theworkpiece and detachment of the leading portion from the trailingportion;

FIG. 6 is a partial fragmentary, cross-sectional, side elevational viewsimilar to that as shown in FIG. 5 and further illustrating an alternateembodiment of the interference assembly; and

FIG. 7 is a partial fragmentary, cross-sectional, side elevational viewsimilar to that as shown in FIGS. 5 and 6 illustrating a secondalternate embodiment of the interference assembly.

DESCRIPTION

While the present invention may be susceptible to embodiment indifferent forms, there is shown in the drawings, and herein will bedescribed in detail, preferred embodiments with the understanding thatthe present description is to be considered an exemplification of theprinciples of the invention and is not intended to limit the inventionto those as illustrated and described herein.

FIGS. 1-3 provide a generalized, diagrammatic, illustration of afastener 20 of the present invention for use in attachment to workpieces22. As shown, the fastener 20 includes a shank 24 defining a centralaxis 26 and a path of travel 27. A drive head 28 is formed on one end ofthe shank 24 and a leading portion in the form of a drill-point portion30 is formed on an end of the shank 24 opposite the drive head 28. Thedrill-point portion 30 drills a hole 31 in the workpieces 22 when thefastener 20 is driven into the workpieces 22. An intermediate portion orthreaded portion 32 is formed on the shank 24 positioned between thedrive head 28 and the drill-point portion 30. A detachment or frangibleportion 34 is shown in the illustrations as including an annular grooveor notch 35 is formed in the shank 24 between the threaded portion 32and the drill-point portion 30. The detachment portion 34 facilitatesthe fracturing and separation of the drill portion 30 from the threadedportion 32 when the threaded portion 32 is engaged in hole 31 formed bythe drill-point portion 30 and the drill point portion engages theopposed wall, FIGS. 2 and 3, which will fracture the frangible portion34.

FIGS. 1-3 provide a series of progressions which show the fastener 20being installed in the workpieces 22 and ultimately in which thedrill-point portion 30 is detached or separated from the fastener 20.Generally, in the method of the present invention, the drill-pointportion 30 of the fastener 20 is driven into a first side 36 of theworkpiece 22 (see FIG. 1) to form the aperture 31. Driving of thefastener is continued with the threaded portion 32 engaging theworkpiece 22. Continued driving results in a tip or point portion 38 ofthe drill-point portion 30 exiting a second side 40 of the workpieces22. A third or opposed surface 42 is positioned proximate the secondside 40 so that the tip 38 will contact the third surface 42 at a severeangle, but does not bore or form a hole therein. As threads 44 areadvanced through the hole 31 formed by the drilling portion 30 (see FIG.2), the tip 38 will engage and be deflected by the third surface 42resulting in the fracturing of the shank 24 at the detachment orfrangible portion 34. Breaking of the shank 24 allows the drill-pointportion 30 to fall away from and be removed from the fastener 20 afterthe fastener 20 is installed, FIG. 4.

The present invention also anticipates a drive tool assembly 48 which isused to drive the fastener 20 of the present invention and effectfracturing of the drill point, when it is not practical to rely upon anopposed surface, such as surface 42 to deflect and fracture the drillpoint. The surface 42 is angled relative to the path of travel of thefastener and may be angled in one of many orientations. In other words,the angle of taper or deflection is sufficient to prevent engagement ofthe drill-point in the surface 42 and thus promotes the deflection andfracturing of the drill-point portion from the threaded portion.

The drive tool assembly 48 as shown in FIG. 5 with alternate embodimentsbeing shown in FIG. 6 (see drive tool 48a) and in FIG. 7 (see drive tool48b). It should be noted, that in the alternate embodiments, features orelements which are identical to those as shown in the embodimentillustrated in FIG. 5 will be represented with the same reference numberand variations of the embodiment will be represented by the samereference numeral with an alphabetic suffix. For example, the drive toolassembly 48 in FIG. 5 is identified in FIG. 6 by reference numeral 48aand in FIG. 7 by reference numeral 48b.

Returning to FIG. 5, the drive tool assembly 48 includes a drivemechanism 50 for producing driving forces for driving the fastener intothe first side 36 of the workpiece 22. In the illustrated embodiment,the drive mechanism is in the form of a standard hand held rotary drill.An engagement tool in the form of a bit 52 is coupled to the drivemechanism 50 and is engageable with the fastener 20 for transferringdriving forces from the driving mechanism 50 to the fastener 20. Aninterference assembly 53 including an interference block 54 is affixedto and depends from the driving mechanism 50. The interference blockincludes a surface portion that equals the third surface 42 discussedabove, against which the fastener is driven to cause the shank 24 tofracture and break at the detachment portion 34 to separate thedrill-point portion 30. The third surface 42 of the interference block54 is positioned near the second side 40 at a predetermined distance topromote detachment of the drill-point portion 30 from the fastener 20.

Having now briefly described the overall structure of the fastener 20and drive tool assembly 48 as well as the method of the presentinvention, we shall now turn to a more detailed description in order tomore fully define the scope of the present invention. As shown in FIG.4, the fastener 20 has been installed in a workpiece 22 to attach apiece of molding or trim material 56 to a body portion 58. The bodyportion 58 includes an upper wall 60 having a flange 61 and a lower wall62 having a flange 63 which are joined by the fastener 20 in anoverlapping area 64. The fastener 20 of the present invention is usefulin this application since only a limited length of shank 24 havingthreads is required in order to attach the trim 56 and to join the upperand lower walls 60, 62. Also, it is advantageous to use theself-drilling type fastener 20 of the present invention to expedite thisassembly and minimize the assembly production cost. However, before thepresent invention, the leading or drill-point portion 30 would remainand would extend from the second side 40.

As shown in FIGS. 1-3, the threaded portion 32 has a length dimension 66and the drill-point portion 30 has a length dimension 68. The threadedportion dimension 66 generally corresponds to a workpiece thickness 70and the drill-point portion dimension 68 is generally less than a gapdimension 72 measured between the second side 40 and the third surface42 which generally define a gap 74 therebetween. It should be noted whenmaking the measurements of the workpiece and third surface 42, themeasurement of the third surface 42 is taken along the central axis 26of the fastener 20 or the path 27 which the fastener travels when thetip 38 contacts the third surface. Considering the foregoing dimensions,a total length 76 of the shank 24 of the fastener 20 is generally lessthan an overall dimension 77 of the workpieces 22 measured between thefirst side 36 and the third surface 42. A differential dimension 78between the overall dimension 77 and the total shank dimension 76 aidsin the deflection of the drill-point portion 30 relative to the thirdsurface 42. As shown in the drawings, it is beneficial to have the thirdsurface 42 disposed at a severe angle 82 relative to the path 27 of thefastener 20. The angle 82 of the third surface 42 serves to preventengagement of the drill portion 30 with the third surface 42 therebypromoting deflection, fracturing and breaking of the shank 24 at thedetachment portion 34, without the drill-point 30 drilling a hole insurface 42.

As shown in FIG. 2, as the fastener 20 is driven into the workpiece 22,the drill-point portion 30 will emerge from the second side 40 with thetip 38 eventually contacting the third surface 42. When the tip 38contacts the third surface 42, the threads 44 have engaged the materialof the workpiece 22 in the hole 31 formed by the drill-point portion 30.The threads 44 provide mechanical advantage to continue to urge thefastener 20 along the path 27 as the fastener 20 is rotated by thedriving mechanism 50. The mechanical advantage provided by the threads44 forces the drill-point portion 30 against the third surface 42. Sincethe tip 38 does not engage the third surface 42, it is deflected ordriven away from the path 27 (as shown by arrow 84 in FIG. 3).

The deflection (84) of the drill-point portion 30 imposes stress uponthe shank 24. Since the detachment or frangible portion 34 is formedwith the notch 35 the stress is concentrated at the detachment portion34 which promotes the fracturing and breaking of the shank 24. Continueddriving separates the shank 24 at the notch 35 with the thread portion32 being retained in the workpieces 22 to achieve its joining orfastening function. It is desirable to form the thread portion 32 withthe dimension 66 generally equal to the thickness 70 of the workpiece 22as this will result in the shank 24 breaking generally flush with thesecond side 40 of the workpieces 22. The differential dimension 78 (seeFIG. 2) is calculated generally be as the smallest dimension whichminimizes the length of the drill-point portion and which promotesfracturing of the shank 24 at the notch 35.

Further considering the notch 35, the notch as shown is an annual grooveformed around the outside surface of the fastener shank 24 in a planegenerally perpendicular to the central axis 26. The notch 35 can beformed at one of many stages of the manufacturing of the fastener 20 andis formed with a notch angle 88 of generally 45 degrees. It isenvisioned that other angles may be used to provide particularadvantages depending on the type of material used to form the fastener,the type of material into which the fastener is installed, the type ofmaterial and angle at which the third surface 42 is disposed, the typeof drive tool assembly 48 and forces applied by such mechanism to thefastener 20, as well as many other factors. It is also understood thatthe detachment or frangible portion 34 may be provided in otherconfigurations such as dimples, surface working without substantialdeformation, as well as any other operation on the detachment portion 34which promotes weakening of the shank 24 so as to produce the breakingfunction as described hereinabove. Additionally, the fastener is formedso that the detachment portion 34 does not result in separation of thedrill-point portion 30 from the threaded portion 32 merely as a resultof the driving torque on the fastener created by the drive mechanism 50.In this regard, it is primarily the deflection (84) in combination withthe rotary forces or torque applied by the drive mechanism to thefastener which promotes the breaking and detachment of the drill-pointportion 30.

The drive tool assembly 48 as shown in FIG. 5 and discussed brieflyabove includes the interference assembly 53 having an interference blockproviding a third surface 42 positioned proximate to the second side 40.The third surface 42 is positioned at an angle 82 to promote deflectionof the drill portion and the breaking of the shank 24 as describedhereinabove. In the embodiment as shown in FIG. 5, the interferenceassembly 53 includes the interference block 54 removably attached to ashaft 92 which is also attached to a collar 94 retained on the drivemechanism 50. The collar 94 is arranged to move axially along the shaft92 thereby allowing the drive mechanism 50 to move toward and away fromthe workpiece 22. Forward and rear stops 96, 98 are attached to theshaft 92 to limit the range of the travel of the collar 94 along theshaft 92 thereby limiting the depth of insertion of fastener 20 into theworkpiece 22 and also retaining the shaft 92 in the collar 94. A handle100 is provided on the shaft 92 to allow an operator to drive the drivemechanism 50 and position the interference block 54 relative to theworkpiece. It should be noted that the arrangement as shown block 54will deflect the drill-point 30 upwardly. The orientation of the block54 may be reversed on shaft 92 so that the surface 42' (opposite surface42) is engaged by the fastener, which will deflect the drill-point 30downwardly, in a manner similar to the embodiment of FIGS. 6 and 7.

As shown in FIG. 5, a first positioning structure 102 is provided on thethird surface 42. The first positioning structure 102 abuts a surface ofthe workpiece 22, in this case an opposing surface 104 of the trim 56.In this arrangement, the dimension between the second side 40 and thirdsurface 42 is sufficient to promote fracturing and breaking of the shank24 at the detachment portion 34. The second and third embodiments of theinterference block 54a, 54b operate in a similar manner.

As shown in FIG. 6, a first positioning structure 102a is provided onthe interference block 54a. The first positioning structure 102a is aprotruding knob 106 formed on an uppermost portion of the interferenceblock 54a. This protruding knob 106 fits into a recess 108 definedbetween the lower wall 62 and the corresponding flange 63. Theprotrusion 106 horizontally positions the third surface 42a of theinterference block 54a in an appropriate position along the fastenertravel path 27. A second positioning surface 110 is provided tovertically position the third surface 42a in the appropriate position.As such, when an operator is using the embodiment as shown in FIG. 6,the interference block 54a is positioned in the recess 108 to providepositive fail safe positioning of the third surface 42a assuring adesired position to promote detachment of the drill portion 30.

In a similar manner, FIG. 7 provides a first positioning structure 102band a second positioning structure 110b which horizontally andvertically position the third surface 42b in an appropriate location inthe fastener path 27. This third embodiment locates a desired horizontalposition by positioning the first positioning structure 102b against anoutside surface 112 of the workpiece 22. The second positioningstructure 110b operates in a similar manner to the correspondingstructure in the second embodiment (FIG. 6) to provide positive verticallocation of the third surface 42b.

The fastener 20, drive tool assembly 48, the system of the fastener anddrive tool assembly 20, 48, and the method of the present inventionpromote the attachment of a self-drilling fastener 20 to workpieces 22and the detachment of the drill-point portion 30 from the fastener 20 asthe fastener 20 is seated in the workpiece. In use, the fastener 20 ispositioned against the first side 36 of the workpiece 22 whereupon thedrive tool assembly 48 operates to rotate the fastener 20 therebyengaging the tip 38 with the first side 36 of the workpiece 22. Thefastener 20 of the present invention is illustrated as drill point typefastener with a chisel point tip 38 which acts to drill the hole 31through the workpiece 22. Next, the threaded portion 32 engages theinside surface of the hole 31 and forms threads therein for secureengagement in the workpiece 22. During the insertion operation the tip38 contacts the third surface 42. At this point, the drill-point portion30 is deflected (84) away from the central axis 26 promoting fracturingand breaking of the shank 24 at the notch 36 in the detachment portion34. Continued driving of the threads 44 through the workpieces 22increases the point interference of the point 38 against the thirdsurface 42 and the fracturing results in breaking of the shank 24.

It should be noted that the drive tool 50 as shown in the illustrationsmay take the form of a variety of drive tools. For example, the drivetool assembly 48 may be embodied in a rotary drill to which the collar94 of the interference assembly 53 is attached as well as a fastener gunwhich allows for rapid, generally automatic, semi-continuous insertionof fasteners. In such a fastener gun, the fasteners may be servedautomatically to the engagement head 52. Additionally, although theabove description discusses the automatic detachment or breaking of thedrill-point portion 30 from the shank 24, it should be understood thatthe drill-point portion may be manually removed from the shank 24 ifnecessary.

While preferred embodiments of the present invention are shown anddescribed, it is envisioned that those skilled in the art may devisevarious modifications and equivalents without departing from the spiritand scope of the appended claims.

The invention claimed is:
 1. A method of fastening a fastener to aworkpiece, said workpiece having a first side and a second side, saidfastener including a shank defining a central axis, a drive head formedon one end of said shank, a drill-point portion located on said shankgenerally opposite said head. a threaded portion located on said shankbetween said head and said drill-point portion and a frangibledetachment portion formed an external surface of said shank between saiddrill-point portion and said threaded portion, said method comprisingthe steps of:driving said fastener to drive said drill-point portioninto said first side of said workpiece; driving said fastener into saidworkpiece with said threaded portion engaging said workpiece until atleast a tip of said drill-point portion exits said second side of saidworkpiece and at least partially extends toward a third surfaceproximate to said second side; placing an interference block proximateto said second surface, said interference block providing said thirdsurface along a driving path of said fastener for creating pointinterference with said tip of said drill-point portion to fracture saiddetachment portion and facilitate the division of said drill-pointportion from said threaded portion; and continuing to drive saidfastener until said tip of said drill-point portion contacts said thirdsurface positioned proximate to said second side causing saiddrill-point portion to detach from said threaded portion at saidfrangible detachment portion.
 2. A method of fastening as recited inclaim 1, said third surface on said interference block being sloped andoriented generally facing said second surface, said method furthercomprising the step of driving said drill-point portion against saidsloped third surface for promoting the fracturing of said fastener atsaid detachment portion to divide said drill-point portion from saidthreaded portion.
 3. A method of fastening a fastener to a workpiece,said workpiece having a first side and a second side, said fastenerincluding a shank defining a central axis, a drive head formed on oneend of said shank, a drill-point portion located on said shank generallyopposite said head, a threaded portion located on said shank betweensaid head and said drill-point portion, and a frangible detachmentportion formed an external surface of said shank between saiddrill-point portion and said threaded portion, said detachment portionfurther comprising a recess formed in said shank between saiddrill-point portion and said threaded portion, said methodcomprisingdriving said fastener to drive said drill-point portion intosaid first side of said workpiece; driving said fastener into saidworkpiece with said threaded portion engaging said workpiece until atleast a tip of said drill-point portion exits said second side of saidworkpiece and at least partially extends toward a third surfaceproximate to said second side; and continuing to drive said fasteneruntil said tip of said drill-point contacts said third surfacepositioned proximate to said second side causing said drill-pointportion to detach from said threaded portion at said frangibledetachment portion.
 4. A method of fastening as recited in claim 3, saidrecess comprising an annular groove formed in an outside surface of saidshank between said drillpoint portion and said threaded portion orientedin a plane generally perpendicular to said central axis.
 5. A fastenerand drive tool system for driving said fastener into a workpiece havinga first surface and a second surface, said fastener having a shank and adrive head formed on one end of said shank;said drive tool having adrive mechanism for producing driving forces for driving said fastenerinto said first side of said workpiece, an engagement bead coupled tosaid drive mechanism for engaging said drive head on said shank of saidfastener, and an interference assembly depending from said drivemechanism, said interference assembly providing a third surfacepositioned proximate to said second side of said workpiece; and saidshank of said fastener defining a central axis, a drill-point portionlocated on said shank generally opposite said drive head, a threadedportion located on said shank between said drive head and saiddrill-point portion, and a detachment portion formed in said shankbetween said drill-point portion and said threaded portion, saiddrill-point portion of said fastener contacting said third surface anddriving thereagainst to promote detachment of said drill-point portionfrom said threaded portion.
 6. A drive tool for driving a fastener intoa workpiece having a first side and a second side; said fastener havinga shank defining a central axis, a drive head formed on one end of saidshank, a drill-point portion located on said shank generally oppositesaid head, and engaging portion located on said shank between said headand said drill-point portion, and a detachment portion formed in saidshank between said drill-point portion and said engaging portion; saiddrive tool comprising:a drive mechanism for producing driving forces fordriving said fastener into said first side of said workpiece; anengagement head coupled to said drive mechanism for engaging said drivehead on said shank of said fastener and transferring driving forces fromsaid drive mechanism to said fastener; and an interference blockassembly depending from said drive mechanism, said interference blockassembly having a third surface positioned proximate to said second sideof said workpiece, said drill-point portion of said fastener contactingsaid third surface and driving thereagainst to promote detachment ofsaid drill-point portion from said engaging portion.
 7. A drive tool asrecited in claim 6, said third surface defining an angle relative tosaid central axis of said fastener when said fastener is driven intosaid workpiece.
 8. A drive tool as recited in claim 7, said interferenceblock assembly further comprising a first positioning structureproviding a first predetermined reference for positioning said toolrelative to said workpiece.
 9. A drive tool as recited in claim 8,further comprising a second positioning structure providing a secondpredetermined reference for positioning said tool relative to saidworkpiece.
 10. A drive tool as recited in claim 7, said interferenceblock assembly further comprising a horizontal positioning structure anda vertical positioning structure for providing a predeterminedhorizontal and vertical positioning reference for positioning said tooland said fastener driven thereby relative to said workpiece.
 11. A drivetool as recited in claim 7, wherein said fastener is threaded and saiddrive mechanism provides rotary driving forces which are transferred tosaid fastener for threadedly engaging said fastener in said workpiece.